Simvastatin, like lovastatin is converted to active metabolites by cytochrome P450 3A4 (CYP3A4). We have shown that lovastatin is susceptible to interactions with a commonly used calcium antagonist, diltiazem, that is known to have the capacity to block CYP3A4. Verapamil can similarly block this enzyme. The current study is to quantify the interaction of diltiazem and of verapamil with simvastatin since combinations of either of these calcium antagonists with simvastatin are likely to occur frequently.